Recently, the number of pixels of a camera module, such as a camera mounted in a mobile phone and a digital camera, has been increasing. With an increase in the number of pixels, miniaturization of pixels is required. Under this situation, such a problem is at issue that there is an absent portion (hereinafter, appropriately referred to as “a defect”) of a digital image signal generated due to a pixel which does not normally function.
In a defect inspection during the manufacture of a camera module, manufactured goods recognized to have defective pixels more than that of the regulations is handled as defective products. As the regulation becomes stricter, the yield of camera modules decreases and thus the manufacturing cost increases. Accordingly, in the related art, a method of obscuring a defect is actively used in which signal processing is performed by a defect correction circuit.
Defect detecting methods are generally classified into two types, a predetection type and a dynamic detection type. The predetection type is a method which detects a defect caused in the process of defect inspection after manufacturing of a camera module and stores address information of the defect in each sensor. The predetection type method is mainly used for the purpose of compensating for a defect by a defect in a multi-layer structure, a leakage current of a floating junction, or the like. The dynamic detection type is a method which detects a defect from a digital image signal during an operation of a camera module. The dynamic detection type method is mainly used for the purpose of compensating for a photodiode-based defect which randomly occurs depending on a temperature characteristic, an exposure time period, etc.
There are some defect correction circuits capable of coping even with a case where two pixels out of 9 (3×3) pixels for the same color are defects (hereinafter, appropriately referred to as two pixel defects). In the case of applying the prediction type method to the case of two pixel defects, problems arise in that there is the limit of address information that can be stored in a circuit in advance and the size of a circuit increases. Further, in the case where an analog gain is high, two pixel defects which are not detected through the defect inspection may come to be noticeable.
In the case of coping with two pixel defects, there is a possibility that not only a target pixel is a defect but also an adjacent pixel of the target pixel is a defect. This reduces the information of adjacent pixels usable for defect detection. As there is less information on the adjacent pixels usable for defect detection, the likeliness of erroneous correction increases. Further, in general, as the amount of incident light increases and an analog gain decreases, it is difficult for two pixel defects to occur and an edge portion is sharper. In this case, applying of strict defect detection and defect correction aimed at the two pixel defects are accompanied by a risk encouraging erroneous correction at an edge portion. Like this, according to the related art, even in the case of coping with two pixel defects by the dynamic detection type method, occurrence of a false color by erroneous correction, a reduction in the resolution, and so on become problems.